He broke out as a junior in 2016, starting 15 games and going 9–2 with a school-record 2.05 ERA, striking out ninety and walking only ten in 105+1⁄3 innings.

[5] After his junior year, Jax was selected by the Minnesota Twins in the third round of the 2016 Major League Baseball draft.

[6] He signed for $645,000 and made his professional debut with the Elizabethton Twins of the Rookie-level Appalachian League, pitching 8+2⁄3 innings.

[13][14] During the season, he pitched for the Fort Myers Miracle of the Class A-Advanced Florida State League, going 3–4 with a 3.70 ERA in 15 games (14 starts).

[17] Jax began 2019 with the Pensacola Blue Wahoos of the Class AA Southern League with whom he was named an All-Star.

[20] In August, Jax was promoted to the Rochester Red Wings of the Class AAA International League, with whom he finished the season.